1. Field of the Invention
The present invention related to a coating process for a rubber wiper and, more particularly, to a coating process for a rubber wiper made of elastomer material, in which a wear-resistant protective coating is formed on the rubber wiper by a chemical and/or physical vapor deposition method from a vaporous coating material generated and activated thermally, by plasma and/or by laser.
2. Prior Art
Known windshield wipers possess a wiper arm incorporating a fastening device secured to a drive shaft, a hinged portion connected therewith by way of a toggle joint, and a wiper rod rigidly secured to the hinged structure. In addition, the windshield wiper possesses a wiper blade, featuring a bearing yoke assembly and a rubber wiper supported by it. The wiper blade is hinged on the wiper arm, whereby a hook-shaped extremity of the wiper rod projects between the two side cheeks of the bearing yoke, embracing a hinged bolt. The articulation constructed in this fashion guides the wiper blade with its rubber wiper over the windshield of the motor vehicle, whereby the hinged portion and the bearing yoke make it possible for the rubber wiper to adapt to the curvature of the windshield. The requisite contact pressure of the rubber wiper upon the windshield of the vehicle is achieved by at least one tension spring, which braces the fastening device and the hinged structure together with the wiper rod by way of the toggle joint.
The rubber wiper consists of an elastomer, for example a natural or synthetic rubber. It has a head cleat connected via a rocker flange with a wiper lip butting against the windshield to be wiped. By way of the rocker flange, the wiper lip is able to shift in inverse direction at the turnabout point of its wiper travel, so as to retain at all times a proper angle to the windshield. When the wiper is activated, the rubber wiper glides over the windshield of the vehicle with its wiper lip, whereby the friction between the lip and the windshield causes the former to abrade. Beyond that, the rubber wiper is subject to environmental factors such as temperature changes, UV radiation, seawater, exhaust gases etc., which may cause premature aging of the materials and enhanced wear.
In principle, wear can be reduced by improved gliding properties, reduced friction and/or harder rubber wipers. German patent DE 26 23 216 describes rubber wipers initially halogenated with chlorine or bromine in a chemical wet hardening process and subsequently treated with a moderate to strongly alkaline solution at temperatures up to 100.degree. C.
After producing the rubber wiper, for example by extrusion, it features a proper, smooth surface. The chemical wet hardening process affects the rubber wiper in its entirety, so that its material properties change, even where that is not required or is very undesirable. Beyond that, its microstructure and macrostructure are altered, for example by chlorine and heat. As a rule, the rubber turns coarser and more brittle, impairing its contact with the windshield and its wiping efficacy. In addition, there is a danger that small or larger particles may break out of the rubber wiper in wiping the windshield. Moreover, for proper cleansing quality, the wiper lip should quickly and easily flip over in reversing its travel direction, without significant resistance. Yet, with harder and more brittle material, its resistance is increased, impeding or at least retarding the reversal process, and there is a tendency for the wiper blade to rattle.
Belgian patent BE 84 8 964 A describes a coating process apt to improve the gliding properties after a hardening process. Accordingly, the rubber wiper receives at least in the area of the lip, by a chemical wet process, a coating which is softer than the base material and is therefore not particularly resistant to wear.